This project involves utilization of single neuron recording techniques in behaving monkeys to study brain mechanisms underlying volitional motor performance. Monkeys are trained to make precise movements of a handle whose rotation controls a visual display. There is intense motor cortex activity for even the smallest of these voluntary movements, with the proportion of motor cortex neurons involved in the control process being much greater than the proportion of spinal cord motoneurons involved in such movements. We have found that there is a reflex negative feedback pathways which stabilizes outputs of motor cortex neurons controlling small precise movements, but that there are internally generated central programs which can overcome reflex feedback when a subject wishes to carry out a movement which runs counter to "hard-wired" reflex inputs.